Whipstocks have long been used to divert a milling tool to cut a new opening through a casing. Typically in these installations, a packer is set in the casing which has a lug or some other guide mechanism to orient the whipstock. The plug or packer is set in the casing and then the whipstock is secured to the packer in the appropriate orientation for the new deviated path to be milled and ultimately drilled. A milling tool is then used to cut through the casing. Having cut through the casing, the milling tool is removed to the surface and drilling with the appropriate bit commences.
Various designs of whipstocks and mounting systems therefor are illustrated in U.S. Pat. Nos. 2,506,799; 5,154,231; 3,397,746; 5,335,737; 5,341,873; and 5,115,872.
U.S. Pat. Nos. 5,156,220; 5,090,481; 4,991,654; and 4,880,059 illustrate the use of sliding sleeves which can be selectively opened to exposed perforations in a casing, which can then permit flow into the casing. The Brandel U.S. Pat. No. 4,991,654 illustrates the use of disintegratable plugs in the openings. U.S. Pat. Nos. 4,397,360 and 4,807,704 illustrate the use of whipstocks to create lateral wellbores from the main wellbore.
It should be noted that some casings, particularly in deviated wellbores, may not be cemented. Casing packers mounted externally to a section or sections of casing can be used to isolate the casing from the wellbore.
The drawback of the current designs is that a separate mill must be employed to cut through the casing, which must then be retracted to the surface so that a drillbit can be mounted to allow the drilling to continue into the formation. The apparatus of the present invention seeks to eliminate the milling step by providing a casing with a sleeve shiftable between an open and closed position to selectively open a window in the casing. The window may be closed during the cementing operation and may be subsequently opened for forming the deviated wellbore off of the whipstock. Should it be desired, the sleeve can, anytime after the drilling of the deviated wellbore and production therefrom, be fully closed. The whipstocks that can be employed with this system can be mounted from the casing directly and can also feature a bore therethrough to allow production from pay zones below the whipstock.